Historical and Contemporary DNA Indicate Fisher Decline and Isolation Occurred Prior to the European Settlement of California

Abstract

Establishing if species contractions were the result of natural phenomena or human induced landscape changes is essential for managing natural populations. Fishers (Martes pennanti) in California occur in two geographically and genetically isolated populations in the northwestern mountains and southern Sierra Nevada. Their isolation is hypothesized to have resulted from a decline in abundance and distribution associated with European settlement in the 1800s. However, there is little evidence to establish that fisher occupied the area between the two extant populations at that time. We analyzed 10 microsatellite loci from 275 contemporary and 21 historical fisher samples (1880–1920) to evaluate the demographic history of fisher in California. We did not find any evidence of a recent (post-European) bottleneck in the northwestern population. In the southern Sierra Nevada, genetic subdivision within the population strongly influenced bottleneck tests. After accounting for genetic subdivision, we found a bottleneck signal only in the northern and central portions of the southern Sierra Nevada, indicating that the southernmost tip of these mountains may have acted as a refugium for fisher during the anthropogenic changes of the late 19th and early 20th centuries. Using a coalescent-based Bayesian analysis, we detected a 90% decline in effective population size and dated the time of decline to over a thousand years ago. We hypothesize that fisher distribution in California contracted to the two current population areas pre-European settlement, and that portions of the southern Sierra Nevada subsequently experienced another more recent bottleneck post-European settlement.

Demographic loss, genetic structure and the conservation implications for Indian tigers

“…A few recent studies [17,55,61] have demonstrated changes in population structure between historical and modern populations. However, all have been relatively limited in their geographical scale, and have only investigated microsatellite genetic variation.…”

“…Additionally, several studies on historical genetic variation reveal that despite major bottlenecks, genetic variation is often comparable between modern and historical samples (e.g. fisher [55]; otter [56]; right whale [57]), while some studies reveal a relatively moderate loss of genetic variation (Scandinavian wolf [11]; puma [16,17]). …”

Effective Population Size, Genetic Variation, and Their Relevance for Conservation: The Bighorn Sheep in Tiburon Island and Comparisons with Managed Artiodactyls

“…Moreover, it allows variation on parameters from one locus to the next one (as different mutation rates), so it is suitable for multilocus microsatellite analyses. In addition, it has been used to estimate population size changes of several species, including lemurs [58] and martens [59]. Finally, this method has demonstrated its robustness for detecting past population size changes [60].…”

Landscape genetics in a changing world: disentangling historical and contemporary influences and inferring change

“…Tucker et al . () used limited historical samples and more numerous contemporary samples for fisher ( Pekania pennanti ) to evaluate whether contemporary fragmentation was due to anthropogenic or long‐term historical processes. However, sample sizes for historical samples remain the primary limitation to a more full‐fledged LG approach, where 50–100 samples may be a minimum for individual‐based analyses (Anderson et al .…”